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In Java Concurrency in Practice, the authors write:
When locking is contended, the losing thread(s) must block. The JVM can implement blocking either via spin-waiting (repeatedly trying to acquire the lock until it succeeds) or by suspending the blocked thread through the operating system. Which is more efficient depends on the relationship between context switch overhead and the time until the lock becomes available; spin-waiting is preferred for short waits and suspension is preferable for long waits. Some JVMs choose between the two adaptively based on profiling data of past wait times, but most just suspend threads waiting for a lock.
When I read this I was quite surprised. Are there any known JVMs implementing blocking either on always spin-waiting or sometimes spin-waiting due to profiling results? It's hard to believe for now.
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Spinlock is a locking system mechanism. It allows a thread to acquire it to simply wait in loop until the lock is available i.e. a thread waits in a loop or spin until the lock is available. Spinlock is held for a short period of time.
SpinLock might be useful when a lock on a shared resource is not going to be held for very long. In such cases, on multi-core computers it can be efficient for the blocked thread to spin for a few cycles until the lock is released. By spinning, the thread does not become blocked, which is a CPU-intensive process.
A lock may be a more flexible and complicated thread synchronization mechanism than the standard synchronized block. A lock may be a tool for controlling access to a shared resource by multiple threads.
Here is evidence that JRockit can use spinlocks - http://forums.oracle.com/forums/thread.jspa?threadID=816625&tstart=494
And if you search for "spin" in the JVM options listed here you will see evidence for the use of / support for spinlocks in Hotspot JVMs.
And if you want a current example, look at "src/hotspot/share/runtime/mutex.cpp" in the OpenJDK Java 11 source tree.
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